The "built in" type 'a ref is implemented using a record with a mutable
field. This example from the manual is simply showing you how to implement
references using an object with a mutable instance variable instead. There
is no language construct "class ref", you are just defining a class that
happens to be named "ref". Since "ref" is just a normal identifier, not a
keyword, this is allowed.

On Tuesday, December 22, 2015, 沈胜宇 <syshen@nudt.edu.cn> wrote:

> Dear all:
>
> In ref manual of ocaml "3.10 Parameterized classes", there is a code
> segment liek this:
>
> class ref (x_init:int) =
> object
> val mutable x = x_init
> method get = x
> method set y = x <- y
> end;;
>
> so what is the meaning of class ref?
>
>
> Shen
>